New Homocamptothecin Payload Simplifies ADC Drug Design
- Camptothecin-class payloads such as DXd currently dominate antibody-drug conjugate (ADC) design, powering approved drugs in the Enhertu family.
- Researchers created a new homocamptothecin analog, H2, built around a simplified seven-membered-ring (hydroxybutyl) core that avoids the lengthy, multi-step F-ring synthesis required for DXd-type payloads.
- H2 retained potent intrinsic cytotoxicity while showing markedly better resistance to hydrolytic breakdown than earlier homocamptothecin designs.
- Trastuzumab-based ADC candidates carrying H2 produced strong bystander-killing effects and antiproliferative activity in vitro, mirroring T-DXd.
- In a HER2-positive xenograft tumor model, the H2-based conjugates matched the antitumor efficacy of the benchmark payload T-DXd.
- The results position the simplified homocamptothecin scaffold as a promising, more synthetically accessible class of next-generation ADC payloads.
• Mechanistically nothing new — H2 is still a topo-I poison in the DXd lineage, so this is a manufacturing/route paper more than a pharmacology one, and that's fine by me. • The real value is ditching the multi-step F-ring synthesis: a payload that matches DXd's potency but scales more cleanly wins on cost-of-goods and batch consistency, which matter as much as IC50 once you're past discovery. • Better hydrolytic stability is the number I'd chase — payload/linker instability in circulation usually hurts therapeutic index more than intrinsic potency does. • "Matched T-DXd" in one xenograft tells you efficacy is in the ballpark, not that PK, tolerability, or TI are equivalent — I want linker compatibility data (cleavable vs. non-cleavable), DAR optimization, and real in vivo tox before calling this a DXd alternative. • Good to see payload diversification beyond DXd/MMAE regardless — worth banking as backup chemistry even pre-clinic.
Homocamptothecin Payloads with Enhanced Potency for Antibody-Drug Conjugates ↗